A downtown Springfield office building was locked down Tuesday after the office that handles Gov. Pat Quinn’s mail received a threatening letter with a suspicious powder.

Authorities eventually determined that the substance was harmless baby powder, but about two-dozen workers inside the building at 222 S. College St. had to spend a little over two hours in their offices as members of the Springfield Fire Department’s hazardous materials unit tested the powder.

Springfield Fire Chief Ken Fustin, speaking before tests confirmed the powder was harmless, said authorities were taking the threat seriously.

“Hazmat team members from the Springfield Fire Department went in wearing protective gear,” Fustin said. “They’ve looked at the contents of the letter as well as what was written on the letter. We feel this is a legitimate threat so we are treating it accordingly.”

The office that received the letter was the Governor’s Office of Citizen Assistance. That office receives the phone calls, e-mails and mail that the governor receives from the public.

The citizen assistance office is just one office in the building at 222 S. College St.

After the workers discovered the powder and called the fire department about 10:30 a.m., the ventilation system was turned off and workers in other offices were told to remain where they were.

About four or five workers that had contact with the letter were isolated.

Fustin declined to elaborate on what the letter said.

Lawmakers were at the Capitol nearby, preparing to debate possible pension-reform legislation. It was unclear if the letter was in any way connected to today’s vote.

The incident remains under investigation by law enforcement officials.

John Reynolds can be reached at 788-1524. Follow him at twitter.com/JohnReynoldsSJR